The present invention relates to optics, and, more particularly, to an integrated-optic out-coupler that comprises an optical waveguide, at least one diffractive Bragg grating (DBG) and a photorefractive material substrate in which the optical waveguide and DBG(s) are integrated.
xe2x80x9cFree-space opticsxe2x80x9d is a phrase often used to describe a technology in which three-dimensional (3-D) discrete optical components, such as prisms and lenses, are used to operate on light in a particular manner for a particular purpose. These discrete optical components are often combined in a particular configuration to operate on light in a particular manner to produce a particular optical effect. Due to the 3-D nature of these discrete optical components, light propagates through them over distances of millimeters or centimeters and thus the configuration is referred to as being on a xe2x80x9cmacroscopicxe2x80x9d scale. These discrete optical components are also commonly referred to as xe2x80x9cbulkxe2x80x9d optical components.
It is known to create macroscopic optical out-couplers using these bulk components. The term xe2x80x9coptical out-couplerxe2x80x9d in this context simply means that the device formed by the bulk component(s) receives light coupled into it and couples at least some fraction of the received light out of the device. This xe2x80x9cout-couplingxe2x80x9d of light can be useful for many purposes, such as, for example, filtering, attenuating, equalizing, or merely redirecting light.
Due to the ever increasing need to provide a capability for performing these types of operations on a xe2x80x9cmicroscopicxe2x80x9d scale (i.e., on the order of micrometers), integrated optical circuits have been developed that have optical elements that are integrated together in a substrate material to form an optical integrated circuit (OIC). These OICs are often referred to as xe2x80x9chybridxe2x80x9d OICs because the actual packaged OIC typically includes optical components that are not integrated, but which are included in the packaged system to enable communication with the integrated optical circuit. A fiber-to-waveguide structure is an example of a component often included in the OIC package for this purpose. Such structures are needed for a variety of reasons, such as, for example, to couple integrated optical waveguides to external optical fibers (i.e., to fibers that are external to the OIC package). In this sense, the OICs are viewed as not being fully integrated and are therefore referred to at times as hybrid ICs.
In these types of OICs, 3-D integrated optical configurations can be built by combining, or xe2x80x9cstackingxe2x80x9d, material layers that have two-dimensional (2-D) integrated optical sub-systems. To provide the optical connection between these stacked layers, optical out-couplers can be used. One of the current disadvantages of OICs is associated with the difficulties of fabrication and packaging. For example, corrugated surfaces formed in one or more of the layers (such as relief surface structures) present difficulties when bonding 2D-layers together. Since the packaging of the OIC can represent a large percentage of the overall costs associated with producing the IC, it is desirable to reduce the difficulties associated with packaging, which generally translates into reduced packaging costs.
Accordingly, a need exists for fully-integrated-optic device that is capable of operating on light on a microscopic scale and that can be created without having to combine material layers having 2-D elements formed therein to obtain 3-D optical configurations. By enabling a fully-integrated-optic device to be created without having to combine material layers, the aforementioned difficulties and high costs associated with creating and packaging OICs can be avoided.
The present invention provides an integrated-optic out-coupler device that comprises a photorefractive substrate, an optical waveguide channel and at least one diffractive Bragg grating. The optical waveguide channel and at least one diffractive Bragg grating are integrated in the substrate. The diffractive Bragg grating intersects the optical waveguide channel and causes at least a fraction of light propagating along the optical waveguide channel to be coupled out of the waveguide.
The present invention also provides a method of out-coupling light out of the plane of the optical waveguide. The method comprises the steps of providing an integrated-optic out-coupler device, coupling light into an optical waveguide channel formed in a photorefractive substrate of the integrated-optic waveguide device and operating on the light propagating along the optical waveguide channel with at least one DBG that has been formed in the substrate to cause at least a fraction of the light to be coupled out of the optical waveguide channel.
The present invention also provides a method for creating an integrated-optic device. The method comprises the steps of providing a photorefractive substrate, forming at least one optical waveguide channel in the substrate and forming at least one diffractive Bragg grating in the substrate such that said at least one diffractive Bragg grating intersects said at least one optical waveguide channel.
In contrast to the known xe2x80x9chybridxe2x80x9d OICs, the present invention provides a fully-integrated-optic device that is capable of operating on light on a microscopic scale and that can be created without having to combine material layers having 2-D elements formed therein to obtain 3-D optical configurations. By enabling a fully-integrated-optic device to be created without having to combine material layers, the aforementioned difficulties and high costs associated with creating and packaging OICs can be avoided.
Furthermore, another advantage of using a photorefractive substrate is that it makes the integrated-optic device re-writable, which means that it is re-programmable. In other words, a holographically-defined DBG that has been written into the substrate can be erased from the substrate and a new holographically-defined DBG can be written into the substrate. This feature of the present invention enables the integrated-optic device to be re-programmed so that the manner in which it operates on light, as well as the wavelength(s) of light on which it operates, can be altered. Therefore, the integrated-optic device can be programmed and re-programmed to serve different purposes, which reduces or eliminates the need to replace the device.